A known form of spring interior comprises a plurality of longitudinally extending bands of springs disposed side by side and connected together by helical wires which extend transversely of the bands and embrace portions of the bands. Several kinds of bands of springs have been proposed for incorporation in spring interiors. One kind of band, which is the subject of British patent No. 1,104,884, will hereinafter be referred to as a band of interlocked springs. It comprises a single length of spring wire shaped to form a plurality of individual coil springs arranged in a row, one end turn of each coil spring lying adjacent to a top face of the band and the other end turn of each coil spring lying adjacent to a bottom face of the band, each coil spring being of a rotational hand opposite to the rotational hand of the adjacent coils immediately before and after it in the row, and being joined to the adjacent coil springs by a pair of interconnecting segments of wire integral with the coil springs. One of the pair of interconnecting segments is located in the bottom face of the band, and the other of the pair of interconnecting segments is located in the top face of the band. Each interconnecting segment comprises a bridging portion or section between adjacent coils, which bridging portion extends lengthwise of the row.
When bands of interlocked springs of the type described hereinabove, and more completely described in the above-identified British patent, are assembled together to form a spring interior, they are disposed side by side and interconnected by helical lacing wires, some of which lie in the top face of the spring interior and others of which lie in the bottom face thereof, the top and bottom faces of the spring interior being the faces defined by the top and bottom faces of the bands incorporated in the spring interior. Each helical wire extends across the bands of springs and embraces end portions of the interconnecting segments of the bands, which end portions extend transversely of the bands from the ends of the bridging portions. In the top face of the spring interior the helical wires are disposed at uniform intervals along the bands of springs, the arrangement being such that there are two springs disposed in the interval between each helical wire and the next. There is a similar arrangement in the bottom face of the spring interior.
The top face of a spring interior assembled in the manner described hereinabove has the general appearance of a rectangular grid. Each of the transverse elements of the grid comprises a helical wire, and each of the longitudinal elements of the grid comprises a row of mutually aligned bridging portions. Within the confines of each rectangle of the grid and disposed a little lower than the grid are the upper end portions of two adjacent coil springs, those two springs constituting parts of the same band of springs. The bottom face of the spring interior is, of course, similar to the top face, though inverted.
A characteristic of the spring interior described in British patent No. 2,143,731, as well as all spring interiors heretofore made from bands of interlocked springs, is that the bridging portions of the interconnecting segments between adjacent springs in one face, e.g. the bottom face, of the spring unit are offset by approximately one spring diameter from the interconnecting segments in the other face, e.g. the top face, of the spring unit. As a consequence of this offset relationship of the interconnecting segments, the endmost interconnecting segments in one face of the spring unit terminate in one-half of an interconnecting segment, while the endmost segment in the other face terminates in a full interconnecting segment. It is desirable that the length of wire contained in the half-length interconnecting segment be sufficient to form an attachment for fixing the endmost portion of the interconnecting segment to the perimeter or border wire which surrounds each face of the spring unit and still locate that border wire immediately above or below the other border wire attached to the full-length interconnecting segment. Because the formed half-length of the interconnecting segment in one face is generally not exactly one spring diameter in length, the border wire connected to that half-length of interconnecting segment is generally not parallel to or located immediately above or below the other border wire.
In order to overcome the natural zig-zag or offset configuration of the bridging portions of bands of interlocked springs which results from the interconnecting segments emerging on opposite sides of a common helical lacing wire one-half pitch apart, a spring interior has been proposed in U.S. Pat. No. 4,942,636, which employs interconnecting segments in which each band of springs has the interconnecting segments shaped with radii of different dimensions at the corners or intersections between the bridging portions and the end portions of interconnecting segments. U.S. Pat. No. 4,942,636 is expressly incorporated herein by reference. By providing substantially differing radii at the two corners of the interconnecting segment formed by the intersection of the bridging portion and the two end portions, the bridging portions of adjacent commonly laced interconnecting segments are axially aligned even though the end portions of those interconnecting segments project from the common lacing helical half a pitch apart along the length of the helical lacing wire. These differing radii "make up" the half-pitch difference in projection, and thus permit the bridging portions of the interconnecting segments to be colinearly aligned and located perpendicular to the axes of the helical lacing wires. Not only does this difference in radii enable the bridging portions of a band of springs to be colinearly aligned and located perpendicular to the helical lacing wires, but it also corrects the misalignment of the vertical axes of adjacent pairs of coil springs of a common band of springs which had heretofore characterized the prior art. The result is an assembled spring interior which is not subject to excessive stresses when the unit is deflected and which therefore is much more durable than prior art spring interiors formed from bands of interlocked springs. This modification also results in the longitudinal side edges of the spring interior being vertically aligned with one another on the top and bottom faces of the spring interior.
In order to overcome the problem of misaligned upper and lower border wires resulting from half-length interconnecting segments being connected to a border wire in one face of the spring unit and full-length interconnecting segments being connected to the border wire in the other face, the spring interior employs an interconnecting segment in one face which is severed at a point half way along its length and formed into a shape conducive to attachment to the border wire. In order that that border wire which is attached to the half-length interconnecting segment may be parallel to and located immediately above or below the border wire in the other face, an adjustment to the length of the interconnecting segment located immediately adjacent to the half-length interconnecting segment is made. This adjustment is made by flattening the supporting structure of the other bridging portions of the interconnecting segment in the face of the band of springs containing the half-length bridging segment. Alternatively, others of the bridging portions of interconnecting segments in the other face may be shortened by gathering in the supporting structure of bridging portions of interconnecting segments in that other face such that the overall length of the bands in both faces are identical and the border wires in one face overlie or underlie the border wire in the other face. In practice, any number of adjustments in the length of the interconnecting segments may be made by flattening or gathering in the supporting structure of one or more bridging portions of the bands so as to extend or reduce the face length of the bands of springs so as to locate one border immediately over the other and maintain the parallelism of the border wires.
The spring interior disclosed in U.S. Pat. No. 4,942,636 comprises a plurality of bands of springs, each band of which comprises a single length of wire shaped to form a plurality of individual coil springs arranged in a longitudinal row with one end turn of each coil spring lying adjacent to a top face of the band, and the other end turn lying adjacent to a bottom face of the band. Each coil spring is joined to the adjacent coil springs by interconnecting segments integral with the coil springs such that one of the interconnecting segments is located substantially in the top face of the band, and the other of the interconnecting segments is located substantially in the bottom face of the band. Each interconnecting segment comprises a bridging portion which extends longitudinally of the row and end portions which extend transversely of the rows. The bands are disposed side by side so that their top faces lie in a top main face of the spring interior and their bottom faces lie in a bottom main face of the spring interior. The bands are interconnected by helical lacing wires lying in the top and bottom faces of the bands and extending across the bands with each helical wire embracing adjacent end portions of the interconnecting segments of the bands. Each of the bridging portions of the interconnecting segments are connected at the ends to end portions of the interconnecting segments by radiused corners of substantially different radii so as to position adjacent bridging portions in substantially longitudinal alignment perpendicular to the helical lacing wires. The bridging portions of the edgemost bands of springs are connected to the border wire by wrapping laterally extending portions of the bridging portions about the border wire and by wrapping of the endmost end portions of the interconnecting segments of the bands of springs about the border wire. Additionally, the endmost bridging portions of the bands are severed at the midpoint of the endmost bridging portion of the band and being connected at the severed end to one of the border wires in one of the main faces of the spring interior, and others of the bridging portions of springs containing that midpoint severed bridging portion having the laterally extending portion of the bridging portion altered in configuration to change the length of those other bridging portions to thereby conform the overall length of the band in one main face of the spring interior to the length of the band in the other face.
Machines and methods for the manufacture of spring interiors and for the forming of springs and spring bands are disclosed in the following patents and patent publications hereby expressly incorporated herein by reference:
British Patent No. 1,095,980;
British Patent No. 1,104,884;
British Patent No. 1,183,315;
British Patent Application No. 8,712,969 filed Apr. 6, 1986, PCT/GB87/00381, International Publication No. WO 87/07541 published Dec. 17, 1987; and
U.S. Pat. No. 4,886,249.
With the machines of the prior art, including those set forth in the patent documents incorporated above, spring interiors of the type discussed above are formed from a plurality of preformed spring bands, usually supplied in the forms of continuous spools, which are fed to an assemblying apparatus. With the prior art methods and apparatus, the spring bands have the bridging portions between consecutive spring coils formed in a forming operation prior to being supplied to the assemblying apparatus by which the bands are laced together and cut to form a spring interior. As such, the supporting structure of the bridging portions of the band, or "nose" as this supporting structure is sometimes called, is preformed to some predetermined dimension and shape which is predetermined by fixed dies in the spring band forming apparatus. The spring bands so formed are then supplied in coils to the spring interior assemblying apparatus. As a consequence, variations in the shape of the bridging portions are very difficult to accurately achieve. This is particularly of consequence when the size of the spring interior being manufactured and the dimensional tolerances of the bands and the assembly operation are not always precisely predicted when the spring bridging portions must be formed.
In addition, the assemblying machines of the prior art have typically performed the lacing function which transversely ties the plurality of bands together by feeding precut lacing springs from a supply magazine. This procedure requires the preforming of various lengths of lacing springs to accommodate the various widths of product being formed. Accordingly, the supplies must be changed and replenished, thus requiring a certain amount of labor and handling in the assembly operation.
With the assemblying apparatus of the prior art, spring interiors having the advantages of those disclosed in U.S. Pat. No. 4,942,636 present a certain difficulty and inefficiency in their manufacture. Accordingly, there is a need to provide an apparatus which is capable of precisely and efficiently manufacturing springs having the advantages of those disclosed in U.S. Pat. No. 4,942,636.